U.S. patent number 4,552,214 [Application Number 06/592,378] was granted by the patent office on 1985-11-12 for pulsed in situ retorting in an array of oil shale retorts.
This patent grant is currently assigned to Gulf Oil Corporation, Standard Oil Company (Indiana). Invention is credited to John M. Forgac, George R. Hoekstra.
United States Patent |
4,552,214 |
Forgac , et al. |
November 12, 1985 |
**Please see images for:
( Certificate of Correction ) ** |
Pulsed in situ retorting in an array of oil shale retorts
Abstract
Greater product yield and quality and continuous upgrading of
shale oil with hydrogen-rich, purge mode off gases is attained by
pulsing in situ retorts at different phases and intervals. In the
process, flow of feed gases to the flame fronts of underground
retorts are sequentially stopped and purged while continuously
retorting the oil shale to enhance transfer of sensible heat from
the combustion zones to the retorting zones and enlarge the
separation between the combustion zones and the advancing fronts of
the retorting zones. The flame fronts can be purged with steam,
water, carbon dioxide, nitrogen, hydrogen, combustion mode off
gases, purge mode off gases, reactor off gases, or combinations
thereof. The combustion mode off gases and/or purge mode off gases
can also be used as part of the feed gas or fuel gas.
Inventors: |
Forgac; John M. (Elmhurst,
IL), Hoekstra; George R. (Wheaton, IL) |
Assignee: |
Standard Oil Company (Indiana)
(Chicago, IL)
Gulf Oil Corporation (Chicago, IL)
|
Family
ID: |
24370424 |
Appl.
No.: |
06/592,378 |
Filed: |
March 22, 1984 |
Current U.S.
Class: |
166/259; 166/260;
166/261; 166/266 |
Current CPC
Class: |
E21B
43/247 (20130101); C10G 1/02 (20130101) |
Current International
Class: |
C10G
1/02 (20060101); C10G 1/00 (20060101); E21B
43/247 (20060101); E21B 43/16 (20060101); E21B
043/247 (); C10B 057/20 () |
Field of
Search: |
;166/261,260,259,263,266,267 ;299/2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Novosad; Stephen J.
Attorney, Agent or Firm: Tolpin; Thomas W. McClain; William
T. Medhurst; R. C.
Claims
What is claimed is:
1. A process for retorting oil shale, comprising the steps of:
(a) simultaneously heating rubblized masses of oil shale in
retorting zones of a plurality of underground retorts to a
retorting temperature to liberate hydrocarbons and water from said
oil shale leaving retorted shale containing residual carbon;
(b) combusting said residual carbon in said oil shale in combustion
zones behind said retorting zones in said plurality of underground
retorts with flame fronts fed by a feed gas to provide a
substantial portion of said heating, said flame fronts advancing
generally in the direction of flow of said feed gas;
(c) injecting a purge fluid selected from the group consisting
essentially of steam, water, nitrogen, carbon dioxide, and
combinations thereof, into said plurality of underground retorts to
quench said flame fronts and subsequently reigniting said flame
fronts with said feed gas while continuing to liberate hydrocarbons
and water in said retorting zone;
(d) step (b) being performed in at least one of said underground
retorts at a time when step (c) is performed in at least one other
of said underground retorts; and
(e) withdrawing said liberated hydrocarbons and water from said
underground retorts.
2. A process for retorting oil shale in accordance with claim 1
wherein said retorting zones have leading edges and said leading
edges are advanced when said flame fronts are quenched.
3. A process for retorting oil shale in accordance with claim 2
wherein said leading edges of said retorting zones are spaced a
distance in front of said flame fronts and said quenching followed
by reignition enlarges said distance.
4. A process for retorting oil shale in accordance with claim 1
wherein said water which is withdrawn from said retorts is recycled
and injected into said retorts for use in quenching said flame
fronts.
5. A process for retorting oil shale in accordance with claim 1
wherein said feed gas comprises air and a flame front controlling
fluid selected from the group consisting essentially of steam,
water, recycled off gases, and combinations thereof.
6. A process for retorting oil shale, comprising the steps of:
(a) heating portions of rubblized masses of oil shale in retorting
zones of a set of underground retorts to a temperature from
800.degree. F. to 1200.degree. F. to liberate hydrocarbons and
retort water from said oil shale leaving retorted shale containing
carbon residue;
(b) sequentially combusting said carbon residue in said retorted
oil shale in combustion zones above said retorting zones in said
set of underground retorts for selected periods of time with flame
fronts supported by a combustion-supporting feed gas containing
from 5% to less than 90% by volume molecular oxygen;
(c) pulsing and extinguishing said flame fronts in said retorts at
different intervals and phases relative to each other with purging
fluids selected from the group consisting essentially of nitrogen,
carbon dioxide, steam, water, hydrogen, purge mode off gases,
combustion mode off gases, reactor off gases, and combinations
thereof;
(d) igniting said flame fronts in said retorts between pulses of
said purging fluids with said feed gas; and
(e) withdrawing said liberated hydrocarbons and retort water from
said retorts.
7. A process for retorting oil shale in accordance with claim 6
wherein said purging fluid consists essentially of nitrogen.
8. A process for retorting oil shale in accordance with claim 6
wherein said purging fluid consists essentially of steam.
9. A process for retorting oil shale in accordance with claim 6
wherein said purging fluid consists essentially of retort
water.
10. A process for retorting oil shale in accordance with claim 6
wherein said purging fluid consists essentially of carbon
dioxide.
11. A process for retorting oil shale in accordance with claim 6
wherein said purging fluid comprises water.
12. A process for retorting oil shale in accordance with claim 6
wherein said feed fluid contains from 10% to 30% by volume
molecular oxygen.
13. A process for retorting oil shale in accordance with claim 6
wherein the oxygen content of said feed fluid is varied.
14. A process for retorting oil shale, comprising the steps of:
(a) forming a series of generally upright modified in situ
underground oil shale retorts in subterranean formations of raw oil
shale by
removing from 2% to 40% by volume of said oil shale from said
formations leaving cavities therein,
transporting said removed shale to a location above ground for
surface retorting, and
explosively rubblizing masses of said oil shale substantially
surrounding said cavities to form said series of underground
retorts;
(b) igniting a flame front generally across each of said retorts
with a fuel gas;
(c) pyrolyzing portions of said rubblized raw oil shale in a
retorting zone in each of said underground retorts to liberate
shale oil off gases and raw retort water from said raw oil shale
leaving retorted shale containing residual carbon, said raw retort
water containing oil shale particulates, shale oil, ammonia, and
organic carbon;
(d) advancing said retorting zone generally downwardly in each of
said underground retorts;
(e) combusting residual carbon on said retorted shale in a
combustion zone above said retorting zone in each of said
underground retorts with a flame front;
(f) alternately injecting a flame front-supporting feed fluid and a
frame front-extinguishing purging fluid selected from the group
consisting essentially of steam, purified water, and raw retort
water containing oil shale particulates, shale oil, ammonia, and
organic carbon, into each of said combustion zones while continuing
step (d), said flame front-supporting feed fluid supporting,
igniting and propelling said flame front generally downwardly to
define a combustion mode of operation, said flame
front-extinguishing purging fluid extinguishing said flame fronts
and accelerating transfer of sensible heat from said combustion
zone to said retorting zones to define a purge mode of
operation;
(g) alternating operating some of said underground retorts in a
combustion mode while operating other of said underground retorts
in a purge mode and vice versa; and
(h) withdrawing said liberated shale oil, off gases, and raw retort
water from said series of underground retorts.
15. A process for retorting oil shale in accordance with claim 14
wherein 15% to 25% of said raw oil shale is removed from said
subterranean formations.
16. A process for retorting oil shale in accordance with claim 14
including cooling said combustion zones with said purging fluid to
a temperature greater than 650.degree. F. and less than 800.degree.
F. before reignition.
17. A process for retorting oil shale in accordance with claim 14
wherein said purging fluid consists essentially of raw retort water
containing oil shale particulates, shale oil, ammonia, and organic
carbon, and some of said withdrawn retort water in step (g) is
injected into said retorts for use as said purging fluid in steps
(f) and (g).
18. A process for retorting oil shale in accordance with claim 14
wherein retort water is liberated from said surface retorting and
injected into said underground retorts for use as part of said
purging fluid.
19. A process for retorting oil shale in accordance with claim 14
wherein at least one adjacent pair of said retorts is operated in
the combustion mode while at least one other adjacent pair of
retorts is operated in the purge mode.
20. A process for retorting oil shale in accordance with claim 14
wherein every other retort is in phase in said combustion mode
while the remaining retorts are in an opposite phase in said purge
mode.
21. A process for retorting oil shale in accordance with claim 14
wherein the off gases liberated during the purge mode have a
substantially greater concentration of hydrogen than said off gases
liberated during the combustion mode.
22. A process in accordance with claim 21 wherein said purging mode
off gases are separated from said combustion mode off gases.
23. A process in accordance with claim 22 wherein at least some of
said purge mode off gases are recycled for use as part of said fuel
gas.
24. A process in accordance with claim 22 wherein at least some of
said purge mode off gases are recycled for use as part of said feed
gas.
25. A process in accordance with claim 22 wherein at least some of
said purge mode off gases are fed to a reactor, after at least some
of the contaminants therein have been removed, for use in upgrading
said shale oil.
26. A process in accordance with claim 22 wherein at least some of
said combustion mode off gases are recycled for use as part of said
fuel gas.
27. A process in accordance with claim 22 wherein at least some of
said combustion mode off gases are recycled for use as part of said
feed gas.
Description
BACKGROUND OF THE INVENTION
This invention relates to a process for underground retorting of
oil shale.
Researchers have now renewed their efforts to find alternate
sources of energy and hydrocarbons in view of past rapid increases
in the price of crude oil and natural gas. Much research has been
focused on recovering hydrocarbons from solid
hydrocarbon-containing material such as oil shale, coal and tar
sands by pyrolysis or upon gasification to convert the solid
hydrocarbon-containing material into more readily usable gaseous
and liquid hydrocarbons.
Vast natural deposits of oil shale found in the United States and
elsewhere contain appreciable quantities of organic matter known as
"kerogen" which decomposes upon pyrolysis or distillation to yield
oil, gases and residual carbon. It has been estimated that an
equivalent of 7 trillion barrels of oil are contained in oil shale
deposits in the United States with almost sixty percent located in
the rich Green River oil shale deposits of Colorado, Utah and
Wyoming. The remainder is contained in the leaner
Devonian-Mississippian black shale deposits which underlie most of
the eastern part of the United States.
As a result of dwindling supplies of petroleum and natural gas,
extensive efforts have been directed to develop retorting processes
which will economically produce shale oil on a commercial basis
from these vast resources.
Generally, oil shale is a fine-grained sedimentary rock stratified
in horizontal layers with a variable richness of kerogen content.
Kerogen has limited solubility in ordinary solvents and therefore
cannot be recovered by extraction. Upon heating oil shale to a
sufficient temperature, the kerogen is thermally decomposed to
liberate vapors, mist, and liquid droplets of shale oil and light
hydrocarbon gases such as methane, ethane, ethene, propane and
propene, as well as other products such as hydrogen, nitrogen,
carbon dioxide, carbon monoxide, ammonia, steam and hydrogen
sulfide. A carbon residue typically remains on the retorted
shale.
Shale oil is not a naturally occurring product, but is formed by
the pyrolysis of kerogen in the oil shale. Crude shale oil,
sometimes referred to as "retort oil," is the liquid oil product
recovered from the liberated effluent of an oil shale retort.
Synthetic crude oil (syncrude) is the upgraded oil product
resulting from the hydrogenation of crude shale oil.
The process of pyrolyzing the kerogen in oil shale, known as
retorting, to form liberated hydrocarbons, can be done in surface
retorts or in underground in situ retorts. In situ retorts require
less mining and handling than surface retorts.
In vertical in situ retorts, a flame front moves downward through a
rubblized bed containing rich and lean oil shale to liberate shale
oil, off gases and condensed water. There are two types of in situ
retorts: true in situ retorts and modified in situ retorts. In true
in situ retorts, none of the shale is mined, holes are drilled into
the formation and the oil shale is explosively rubblized, if
necessary, and then retorted. In modified in situ retorts, some of
the oil shale is removed by mining to create a cavity which
provides extra space for explosively rubblized oil shale. The oil
shale which has been removed is conveyed to the surface and
retorted above ground.
In order to obtain high thermal efficiency in retorting, carbonate
decomposition should be minimized. Colorado Mahogany zone oil shale
contains several carbonate minerals which decompose at or near the
usual temperature attained when retorting oil shale. Typically, a
28 gallon per ton oil shale will contain about 23% dolomite (a
calcium/magnesium carbonate) and about 16% calcite (calcium
carbonate), or about 780 pounds of mixed carbonate minerals per
ton. Dolomite requires about 500 BTU per pound and calcite about
700 BTU per pound for decomposition, a requirement that would
consume about 8% of the combustible matter of the shale if these
minerals were allowed to decompose during retorting. Saline sodium
carbonate minerals also occur in the Green River formation in
certain areas and at certain stratigraphic zones. The choice of a
particular retorting method must therefore take into consideration
carbonate decomposition as well as raw and spent materials handling
expense, product yield and process requirements.
While efforts are made to explosively rubblize the oil shale into
uniform pieces, in reality the rubblized mass of oil shale contains
numerous different sized fragments of oil shale which create
vertical, horizontal and irregular channels extending sporadically
throughout the bed and along the wall of the retort. As a result,
during retorting, hot gases often flow down these channels and
bypass large portions of the bed, leaving significant portions of
the rubblized shale unretorted.
Different sized oil shale fragments, channeling and irregular
packing, and imperfect distribution of oil shale fragments cause
other deleterious effects including tilted (nonhorizontal) and
irregular flame fronts in close proximity to the retorting zone and
fingering, that is, flame front projections which extend downward
into the raw oil shale and advance far ahead of other portions of
the flame front. Irregular flame fronts and fingering can cause
coking, burning, and thermal cracking of the liberated shale oil.
Irregular, tilted flame fronts can lead to flame front breakthrough
and incomplete retorting. In the case of severe channeling,
horizontal pathways may permit oxygen to flow underneath the raw
unretorted shale. If this happens, shale oil flowing downward in
that zone may burn. It has been estimated that losses from burning
in in situ retorting can be as high as 40% of the product shale
oil.
Furthermore, during retorting, significant quantities of oil shale
retort water are also producted. Oil shale retort water is laden
with suspended and dissolved impurities, such as shale oil and oil
shale particulates ranging in size from less than 1 micron to 1,000
microns and contain a variety of other contaminants not normally
found in natural petroleum (crude oil) refinery waste water,
chemical plant waste water or sewage. Oil shale retort water
usually contains a much higher concentration of organic matter and
other pollutants than other waste waters or sewage causing
difficult disposal and purification problems.
The quantity of pollutants in water is often determined by
measuring the amount of dissolved oxygen required to biologically
decompose the waste organic matter in the polluted water. This
measurement, called biochemical oxygen demand (BOD), provides an
index of the organic pollution in the water. Many organic
contaminants in oil shale retort water are not amenable to
conventional biological decomposition. Therefore, tests such as
chemical oxygen demand (COD) and total organic carbon (TOC) are
employed to more accurately measure the quantity of pollutants in
retort water. Chemical oxygen demand measures the amount of
chemical oxygen needed to oxidize or burn the organic matter in
waste water. Total organic carbon measures the amount of organic
carbon in waste water.
Over the years, a variety of methods have been suggested for
purifying or otherwise processing oil shale retort water. Such
methods have included shale adsorption, in situ recycling,
electrolysis, flocculation, bacteria treatment and mineral
recovery. Typifying such methods and methods for treating waste
water from refineries and chemical and sewage plants are those
described in U.S. Pat. Nos. 2,948,677; 3,589,997; 3,663,435;
3,904,518; 4,043,881; 4,066,538; 4,069,148; 4,073,722; 4,124,501;
4,178,039; 4,121,662; 4,207,179; and 4,289,578. Typifying the many
methods of in situ retorting are those found in U.S. Pat. Nos.
1,913,395; 1,919,636; 2,481,051; 3,001,776; 3,586,377; 3,434,757;
3,661,423; 3,951,456; 3,980,339; 3,994,343; 4,007,963; 4,017,119;
4,105,251; 4,120,355; 4,126,180; 4,133,380; 4,149,752; 4,153,300;
4,158,467; 4,117,886; 4,185,871; 4,194,788; 4,199,026; 4,210,867;
4,210,868; 4,231,617; 4,243,100; 4,263,969; 4,263,970; 4,265,486;
4,266,608; 4,271,904; 4,315,656; 4,323,120; 4,323,121; 4,328;863;
4,343,360; 4,343,361; 4,353,418; 4,378,949; 4,425,967; and
4,436,344. These prior art processes have met with varying degrees
of success.
It is, therefore, desirable to provide an improved in situ oil
shale retort and process which overcome most, if not all, of the
above problems.
SUMMARY OF THE INVENTION
An improved in situ process is provided to retort oil shale in a
series of underground retorts. In the novel process, some of the
underground retorts are operated in a combustion mode while the
other underground retorts are operated in a purging mode and vice
versa for greater process efficiency and effectiveness. During the
combustion mode, the flame front is ignited and driven through the
retort with a flame front-supporting feed gas. During the purging
mode, the flame front is intermittently stopped and purged to
extinguish the flame front while continuously retorting the oil
shale. This alternate extinguishment and ignition of the flame
front is referred to as "pulsed combustion."
The flame front-supporting feed gas can be air or an oxidizing gas
diluted with steam, water, retort off gases, reactor off gases, or
combinations thereof.
The purge can be steam, water, nitrogen carbon dioxide, hydrogen,
combustion mode off gases, purge mode off gases, reactor off gases,
and combinations thereof. The water purge can be purified water,
condensed steam, or retort water recycled from an underground or an
aboveground retort. Retort water typically contains oil shale
particulates, shale oil, ammonia, and organic carbon.
Pulsed combustion increases product yield and quality. It also
promotes uniformity of the flame front and minimizes fingering and
projections of excessively high temperature zones in the rubblized
beds of shale. When the combustion-sustaining feed fluid is shut
off, combustion stops and burning of product oil is quenched and
the area in which the flame front was present remains stationary
during shut off to distribute heat downward in that bed. Upon
reignition, a generally horizontal flame front is established which
advances in the general direction of flow of the feed gas.
Intermittent injection of the feed gas lowers the temperature of
the flame front, minimizes carbonate decomposition, coking and
thermal cracking of liberated hydrocarbons. The pulse rate and
duration of the feed control the profile of the flame front.
During purging, heat is dissipated throughout the bed where
retorting was incomplete or missed and these regions are retorted
to increase product recovery. Thermal irregularities in the bed
equilibrate between pulses to lower the maximum temperature in the
retort.
During periods of noncombustion, sensible heat from the retorted
and combusted shale advances downward through the raw colder shale
to heat and continue retorting the beds. Continuous retorting
between pulses, advances the leading edge (front) of the retorting
zones and thickens the layers of retorted shale containing
unburned, residual carbon to enlarge the separation between the
combustion and retorting zones when the flame front is reignited in
response to injection of the next pulse of feed gas. Greater
separation between the combustion and retorting zones decreases
flame front breakthrough, oil fires and gas explosions.
During feed gas shutoff, the liberated shale oil has more time to
flow downward and liquefy on the colder raw shale. Drainage and
evacuation of oil during noncombustion moves the effluent oil
farther away from the combustion zone upon reignition to provide an
additional margin of safety which diminishes the chances of oil
fires.
Additional benefits of pulsed combustion include the ability to
more precisely detect the location and configuration of the flame
front and retorting zone by monitoring the change of off gas
composition.
The alternate, sequential, and pulsed mode of operation of this
novel process is particularly useful with a water or steam purge in
providing a substantially continuous supply of hydrogen-rich purge
mode off gases to the hydrotreater or other upgrading reactor for
continuous shale oil upgrading.
As used in this application, the term "shale oil" means oil which
has been obtained from retorting raw oil shale.
The term "retorted oil shale" means raw oil shale which has been
retorted to liberate shale oil, light hydrocarbon gases and retort
water, leaving an inorganic material containing residual
carbon.
The terms "spent oil shale" and "combusted oil shale" as used
herein mean retorted oil shale from which most of the residual
carbon has been removed by combustion.
The terms "oil shale water," "shale water," and "retort water" mean
water which has been emitted during retorting of raw oil shale.
The term "oil shale particulates" as used herein includes
particulates of raw, retorted and combusted oil shale ranging in
size from less than 1 micron to 1,000 microns.
The terms "normally liquid," "normally gaseous," "condensible,"
"condensed," and "noncondensible" as used throughout this
application are relative to the condition of the subject material
at a temperature of 77.degree. F. (25.degree. C.) at atmospheric
pressure.
A more detailed explanation of the invention is provided in the
following description and appended claims taken in conjunction with
the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of a pulsed in situ
retorting process in accordance with principles of the present
invention;
FIG. 2 is a schematic flow diagram of one of the in situ retorts;
and
FIG. 3 is an alternate schematic flow diagram of one of the in situ
retorts with retort oil shale water used as the purge and a
cryogenic processor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A series or set of underground, modified in situ oil shale retorts
10a, 10b, 10c, and 10d (FIG. 1) are arranged in a tier or array in
adjacent subterranean formations 12 of oil shale to produce shale
oil and hydrocarbon gases from raw oil shale. There are at least
two retorts and preferably four or more retorts. For commercial
production, there are at least 30 retorts.
As best shown in FIG. 2, each retort is covered with an overburden
14 and is elongated, upright, and generally box-shaped, with a top
or dome-shaped roof 16. Each retort is filled with an irregularly
packed, fluid permeable, rubblized mass or bed 18 of different
sized oil shale fragments including large oil shale boulders 20 and
minute oil shale particles or fines 22. Irregular, horizontal and
vertical channels 24 extend throughout the bed and along the walls
26 of each retort.
The rubblized mass is formed by first mining an access tunnel or
drift 28 extending horizontally into the bottom of each retort and
removing from 2% to 40% and preferably from 15% to 25% by volume of
the oil shale from a central region of the retort to form a cavity
or void space. The removed oil shale is conveyed to the surface and
retorted in one or more aboveground retorts. The mass of oil shale
surrounding the cavity is then fragmented and expanded by
detonation of explosives to form the rubblized mass 18.
Conduits or pipes 30-35 extend from above ground through overburden
14 into the top of the retorts. The pipes include ignition fuel
lines 30 and 31, feed lines 32 and 33, and purge lines 34 and 35.
The extent and rate of gas flow through the fuel, feed, and purge
lines are regulated and controlled by valves 36, 38, and 40,
respectively. Burners 42 are located in proximity to the top of the
shale beds.
In order to commence retorting or pyrolyzing of the rubblized mass
18 of oil shale, a liquid or gaseous fuel, preferably a combustible
ignition gas or fuel gas, such as recycled off gases or natural
gas, is fed into the retort through the fuel lines 30 and 31 and an
oxygencontaining, flame front-supporting, feed gas or fluid, such
as air, is fed into the retort through the feed lines 32 and 33.
The burners are then ignited to establish a flame front 44
horizontally across the bed 18. If economically feasible or
otherwise desirable, the rubblized mass of oil shale can be
preheated to a temperature slightly below the retorting temperature
with an inert preheating gas, such as steam, nitrogen, or retort
off gases, before introduction of feed fluid and ignition of the
flame front. After ignition, the fuel valve is closed to shut off
inflow of fuel gas. Once the flame front is established, residual
carbon contained in the oil shale usually provides an adequate
source of fuel to maintain the flame front as long as the
oxygen-containing feed gas is supplied to the flame front. Fuel gas
or shale oil can be fed into the retort through the fuel line to
augment the feed gas for leaner grades and seams of oil shale.
The oxygen-containing feed sustains and drives the flame front
downwardly through the bed of oil shale. The feed can be air, or
air enriched with oxygen, or air diluted with a diluent. The
diluent can be steam, recycled retort off gases, purified (treated)
water, condensed steam, or raw oil shale retort water containing
oil shale particulates, shale oil, ammonia, and organic carbon, or
combinations thereof, as long as the feed gas has from 5% to less
than 90% and preferably from 10% to 30% and most preferably a
maximum of 20% by volume molecular oxygen. The oxygen content of
the feed gas can be varied throughout the process.
The flame front emits combustion off gases and generates heat which
moves downwardly ahead of the flame front and heats the raw,
unretorted oil shale in a retorting zone 46 to a retorting
temperature from 800.degree. F. to 1200.degree. F. to retort and
pyrolyze the oil shale in the retorting zone. During retorting, oil
shale retort water and hydrocarbons are liberated from the raw oil
shale. The hydrocarbons are liberated as a gas, vapor, mist or
liquid droplets and most likely a mixture thereof. The liberated
hydrocarbons include light gases, such as methane, ethane, ethene,
propane, and propene, and normally liquid shale oil which flows
downwardly by gravity, condense and liquefy upon the cooler,
unretorted raw shale below the retorting zone, forming condensates
which percolate downwardly through the retort into access tunnel
28.
Retort off gases emitted during retorting include various amounts
of hydrogen, carbon monoxide, carbon dioxide, ammonia, hydrogen
sulfide, carbonyl sulfide, oxides of sulfur and nitrogen, water
vapors, and low molecular weight hydrocarbons. The composition of
the off gas is dependent on the composition of the feed.
Oil shale retort water is formed from the thermal decomposition of
kerogen during retorting and is referred to as "water of
formation." Oil shale retort water can also be derived from in situ
steam injection (process water), aquifers or natural underground
streams in in situ retorts (aquifer water), and in situ shale
combustion (water of combustion).
Raw retort oil shale water, if left untreated, is generally
unsuitable for safe discharge into lakes and rivers or for use in
downstream shale oil processes, because it contains a variety of
suspended and dissolved pollutants, impurities and contaminants,
such as raw, retorted and spent oil shale particulates, shale oil,
grease, ammonia, phenols, sulfur, cyanide, lead, mercury and
arsenic. Oil shale water is much more difficult to process and
purify than waste water from natural petroleum refineries, chemical
plants and sewage treatment plants, because oil shale water
generally contains a much greater concentration of spsended and
dissolved pollutants which are only partially biodegradable. For
example, untreated retort water contains over 10 times the amount
of total organic carbon and chemical oxygen demand, over 5 times
the amount of phenol and over 200 times the amount of ammonia as
waste water from natural petroleum refineries.
Oil shale retort water is laden with suspended and dissolved
impurities including shale oil and particulates of raw, retorted
and/or spent oil shale ranging in size from less than 1 micron to
1,000 microns as well as a variety of other impurities as explained
below. The amount and proportion of the shale oil, oil shale
particulates and other impurities depend upon the richness and
composition of the oil shale being retorted, the composition of the
feed gas and retorting conditions. One sample of retort water from
a modified in situ retort had a pH of 8.9 to 9.1 and an alkalinity
of 12,000 mg/1, and contained 1,800 mg/1 total organic carbon,
7,000 mg/1 chemical oxygen demand, 15,000 mg/1 total solids, 1,600
mg/1 ammonia, 6,000 mg/1 sodium, 7 mg/1 magnesium and 5 mg/1
calcium.
Three other test samples of oil shale retort water from a modified,
in situ retort had the following composition:
______________________________________ Test 1 Test 2 Test 3
______________________________________ COD, mg/l 11174 13862 10140
Phenols, mg/l 29 30 30 Total dissolved solids, mg/l 3159 2151 1099
Total suspended solids, mg/l 718 435 10.8 Organic C, ppm 6660 5640
4220 Inorganic C, ppm 1520 1600 4120 NH.sub.3, ppm 1150 6000 690
Cu, ppm <0.05 <0.05 <0.05 F--, ppm 2 3 1 N, ppm 5200 4700
6970 Ni, ppm 0.38 0.53 0.30 P, ppm 3 <1 852 S, % 0.05 0.05 0.04
Zn, ppm 0.05 0.08 0.08 CN--, ppm <.01 <.01 0.41 Ag, ppm
<0.05 <0.05 <0.05 As, ppm 1.06 0.47 0.5
______________________________________
Another test sample of oil shale retort water from a modified in
situ retort had the following composition:
______________________________________ HCO.sub.3 668 mg/l SCOD 1249
mg/l TOTAL ALKALINITY 1164 mg/l N (TOTAL) 540 mg/l NH.sub.3 392
mg/l NO.sub.3 .41 mg/l F 1.29 mg/l S 53.0 mg/l TOC 281 mg/l PHENOL
14.2 mg/l Shale oil and grease 106 mg/l As .133 mg/l B .23 mg/l
SO.sub.4 1916 mg/l S.sub.2 O.sub.3 426 mg/l SCN 0.17 mg/l CN
<.05 mg/l pH 8.7 ORGANIC-N 80.8 mg/l TRACE ELEMENTS Ba <.1
mg/l Cd <.01 mg/l Cr <.01 mg/l Cu <.01 mg/l Pb <.05
mg/l Hg <.0003 mg/l Mo 0.9 mg/l Sc <.05 mg/l Ag <.01 mg/l
Zn <.01 mg/l ______________________________________
The effluent product stream of condensate (liquid shale oil and
shale oil retort water) and off gases in each retort, flow downward
to the sloped bottom 48 (FIG. 2) of the retort and then into its
own collection basin and separator 50, also referred to as a "sump"
in the bottom of the access tunnel. A concrete wall 52 prevents
leakage of off gas into the mine.
Liquid shale oil, water, purge mode off gases, and combustion mode
off gases are separated in the collection basins by gravity and
pumped to the surface by pumps 54-57, respectively, through inlet
and return lines 58-63, respectively. The pumps can be located
above ground or below ground, as desired.
As best shown in FIG. 1, shale oil from the retorts are combined
and mixed in a single common oil line 64. Retort water from the
retorts are combined and mixed in a common water line 66. Hydrogen
rich purge mode off gases from the retorts are combined and mixed
in a single, common purge gas line 68. Hydrogen lean combustion
mode off gases from the retorts are combined and mixed in a single,
common combustion gas line 70.
In each retort, a purge valve 72 controls the flow of purge mode
off gases. A combustion gas valve 74 controls the flow of
combustion mode off gases. While separate purge mode and combustion
mode gas lines are preferred for best results, it may be desirable
in some circumstances to use, in lieu thereof, a common, single,
purge mode and combustion mode gas line with a single control valve
to selectively direct the flow of off gases to either the common
purge gas line or the common combustion gas line depending on
whether the retort is in a purge mode or in a combustion mode.
Additional valves can be used, if desired, to control the flow of
shale oil and retort water.
Raw (untreated) retort combustion mode off gases can be recycled as
part of the fuel gas or feed, either directly or after light gases
and oil vapors contained therein have been stripped away in a
quench tower or stripping vessel.
During the retorting process, retorting zone 46 (FIG. 2) moves
downward leaving a layer or band 76 of retorted shale with residual
carbon. Retorted shale layer 76 above retorting zone 46 defines a
retorted shale zone which is located between retorting zone 46 and
the flame front 44 of the combustion zone 78. Residual carbon in
the retorted shale is combusted in the combustion zone 78 leaving
spent, combusted shale in a spent shale zone 80.
In order to enhance more uniform flame fronts across the retorts,
the feed gas in the feed lines are fed into the retorts in pulses
by intermittently stopping the influx of feed fluid via the feed
gas control valves to alternately quench and reignite the flame
fronts for selected intervals of time. A purging gas or fluid, also
referred to as a purge gas or fluid, "purge," or "quench," is
injected or sprayed downwardly through the purge lines into the
combustion zones of the retorts in which the inflow of feed gas has
been stopped between pulses of feed. The purge extinguishes,
quenches, and blankets the flame front and accelerates transfer of
sensible heat from the combustion zone to the retorting zone of the
retort.
When the flame front of a retort is purged (extinguished) between
pulses of feed fluid, that retort is operated in a purging or purge
mode of operation. When the flame front of a retort is present and
supported by a feed gas, that retort is operated in a combustion
mode of operation.
In order to provide a substantially continuous supply of
hydrogen-enriched purging-mode off gases to one or more upgrading
reactors 82 for continuous shale oil upgrading operation and in
order to enhance process efficiency, economics, and product
recovery, some of the retorts are operated in the combustion mode
while the other retorts are operated in the purging mode and vice
versa. This sequential pulsing process also provides a
substantially continuous supply of combustion and purge mode off
gases for use as part of the feed gas. During the combustion mode
of a retort, the retort's feed and combustion off gas valves are
open, while the retort's purge and purge mode off gas valves are
closed. During the purge mode of operation of a retort, the
retort's purge and purge mode off gas valves are open, while the
retort's feed gas valves are closed.
In the preferred embodiment, alternate (every other) retorts,
retorts 10a and 10c (FIG. 1) are operated in the combustion mode
while the other retorts 10b and 10d are operated in the purging
mode and vice versa. Retorts 10a and 10c, therefore, operate
together in tandem in the same phase and interval. Retorts 10b and
10d also operate together in tandem in the same phase and interval
but in an opposite phase and interval to retorts 10a and 10c.
If desired, adjacent retorts 10a and 10b can be operated in the
same phase and interval in the combustion mode, while adjacent
retorts 10c and 10d are in the opposite phase and interval in the
purging mode and vice versa. Also, retorts 10a and 10d can be
operated in the same phase and interval, if desired, while retorts
10b and 10c are operated in another phase.
Furthermore, if desired, one of the retorts can be in one phase and
interval while the other retorts are in an opposite phase and
interval. It will be appreciated that other phase combinations,
intervals, and sequences can also be used, if desired.
As shown in FIG. 3, the purge fluid can consist of or comprise raw
(untreated) retort shale water containing oil shale particulates,
shale oil, organic carbon, and ammonia, which has been fed
(recycled) to the purge lines of the retorts by the retort water
lines 61, 84, and 86 via retort water valves 88 and 90. This avoids
the enormous expense of purifying and treating the contaminated
retort water to environmentally acceptable levels and thereby
enhances retorting efficiency and economy. Excess retort water can
be discharged for purification, treatment, and/or further
processing through water discharge line 92 via two-way valve 88,
after closing valves 90 and 94.
The purge fluid can also contain or consist of purified (treated)
water, condensed steam, uncondensed steam, nitrogen, carbon
dioxide, hydrogen, purge mode off gases, combustion mode off gases,
or reactor off gases. Retort water from an aboveground retort can
also be used as the purge. Uncondensed steam is particularly useful
as a purge gas.
Raw (untreated) retort water containing oil shale particulates, oil
shale, organic carbon and ammonia can also be fed (recycled) to the
feed lines of the retorts by lines 61, 84, 96, and 98, upon opening
valves 86 and 88, for use as part of the feed for even greater
retorting economy and efficiency. Retort water from an aboveground
retort can also be fed into the feed lines for use as part of the
feed.
During purging, i.e., between pulses of feed, retorting of oil
shale continues. The purge fluid enhances the rate of downward
advancement of retorting zone to widen the gap and separation
between the leading edge or front of retorting zone and the
combustion zone. Purging also thickens the retorted shale layer and
enlarges the separation between the retorting zone and the
combustion zone. The enlarged separation minimizes losses from oil
burning upon reignition which occurs when the next pulse of feed is
injected. The combustion zone can be cooled to a temperature as low
as 650.degree. F. by the purge and still have successful ignition
with the next pulse of feed.
The injection pressures of the feed and fuel gases, as well as the
purge gas if a gas is used as the purge, is from one atmosphere to
5 atmospheres, and most preferably 2 atmospheres. The flow rates of
the feed, fuel, and purge gases are a maximum of 10 SCFM/ft.sup.2,
preferably from 0.01 SCFM/ft.sup.2 to 6 SCFM/ft.sup.2, and most
preferably from 1.5 SCFM/ft.sup.2 to 3 SCFM/ft.sup.2.
When retort water, treated water, or condensed steam is used as the
purge, the injection pressure of the purge is similar to the feed,
and the flow rate of the purge is from about 0.1 to 3.75
gal/hr/ft.sup.2 (30 lbs/hr/ft.sup.2) and most preferably a maximum
of 0.275 gal/hr/ft.sup.2 (2.2 lbs/hr/ft.sup.2).
The duration of each pulse of feed gas and purge is from 15 minutes
to 1 month, preferably from 1 hour to 24 hours and most preferably
from 4 hours to 12 hours. The time ratio of purge to feed gas is
from 1:10 to 10:1 and preferably from 1:5 to 1:1.
Purge mode off gases produced during purging with steam, retort
water, and treated water have a substantially greater concentration
of hydrogen than combustion mode off gases produced during
combustion with feed gas.
Typical compositions (volume percent dry basis) of combustion mode
off gases and purge mode off gases taken from a modified in situ
retort with a feed gas consisting essentially of air diluted with
steam and a purge gas consisting essentially of steam are shown in
the following table:
______________________________________ Combustion Mode Purge Mode
Off Gases Off Gases ______________________________________ H.sub.2
7.0 48.0 N.sub.2 55.4 1.0 CO 1.2 4.0 CO.sub.2 32.0 41.5 CH.sub.4
1.2 2.8 C.sub.2 H.sub.4 0.1 0.1 C.sub.2 H.sub.6 0.3 0.2 C.sub.3
H.sub.6 0.1 0.1 C.sub.3 H.sub.8 0.1 0.1 C.sub.4 0.2 0.1 C.sub.5 +
0.2 0.1 O.sub.2 0.4 0.0 NH.sub.3 1.1 0.5 H.sub.2 S 0.7 1.5 COS
0.005 0.008 CS.sub.2 0.002 0.003 CH.sub.4 S 0.003 0.004
______________________________________
Hydrogen-rich off gases produced during purging are pumped by a
purge gas pump 56 through gas lines 62, 68, and 100 to one or more
CO.sub.2 scrubbers 102 (FIGS. 1 and 2) where the hydrogen-rich off
gases can be scrubbed of carbon dioxide. Carbon dioxide is removed
from the scrubber through CO.sub.2 line 104 and recycled for use as
part of all of the purge gas or vented to the atmosphere. The
scrubbed hydrogen-rich off gases, which contain at least 70%,
preferably at least 80%, and most preferably at least 95%, by
weight hydrogen, are fed through scrubbed gas line 106 to one or
more upgrading reactors 82, such as hydrotreaters, hydrocrackers,
or catalytic crackers, for use as an upgrading gas in upgrading the
shale oil produced in the retorts.
Fresh, makeup catalyst is fed to the reactor(s) through catalyst
line 108. Shale oil produced in the retorts is fed to the
reactor(s) through shale oil line 59 and/or 64. The reactor(s) can
be a fluid bed reactor, ebullated bed reactor, or fixed bed
reactor.
In the reactor(s), the shale oil is contacted, mixed, and
circulated with the upgrading gas (the scrubbed, hydrogen-rich,
purge mode, off gases) in the presence of the catalyst under
upgrading conditions to substantially remove nitrogen, oxygen,
sulfur, and trace metals from the shale oil in order to produce an
upgraded, more marketable, shale oil or syncrude. Upgraded shale
oil is removed from the reactor(s) through syncrude line 110. Spent
catalyst is removed from the reactor through spent catalyst line
112. Reaction off gases are removed from the reactor(s) through
overhead line 114. The reaction off gases can be recycled for use
as part of the fuel gas, feed gas, or purge, or can be used for
other purposes.
The catalyst has at least one hydrogenating component, such as
cobalt, molybdenum, nickel, or phosphorus, or combinations thereof,
on a suitable support, such as alumina, silica, zeolites, and/or
molecular sieves having a sufficient pore size to trap the trace
metals from the shale oil. Other upgrading catalysts can be
used.
Typical upgrading conditions in the reactor(s) are: total pressure
from 500 psia to 6000 psia, preferably from 1200 psia to 3000 psia;
hydrogen partial pressure from 500 psia to 3000 psia, preferably
from 1000 psia to 2000 psia; upgrading gas flow rate (off gas feed
rate) from 2500 SCFB to 10,000 SCFB, and LHSV (liquid hourly space
velocity) from 0.2 to 4, and preferably no greater than 2 volumes
of oil per hour per volume of catalyst. Hydrotreating temperatures
range from 700.degree. F. to 830.degree. F. Hydrocracking
temperatures range from 650.degree. F. to 820.degree. F.
Hydrogen lean, retort off gases produced in the retorts during
combustion can be pumped by combustion gas pump 58 through
combustion lines 63, 70, and 116 into the fuel gas, feed, or purge
lines for use as part of the fuel gas, feed, and/or purge,
respectively. Alternatively, the hydrogen lean retort off gases can
be fed upstream for further processing or flared for heating
value.
Instead of removing carbon dioxide from the purgemode hydrogen-rich
off gases in a CO.sub.2 scrubber, the purge mode off gas can be
cryogenically processed in a cryogenic processing unit 118 as shown
in FIG. 3 to remove the carbon dioxide and other contaminants
through discharge line 120. In the cryogenic processing unit, the
purge mode off gases are condensed and cryogenically cooled in a
series of cold boxes. Auto-refrigeration supplies the cooling
requirements. The cryogenically processed hydrogen-rich off gases
are fed through line 106 to the upgrading reactor for use as the
upgrading gas. Shale oil is upgraded in the reactor in the same
manner as discussed previously.
While vertical modified-in-situ retorts are used in the preferred
retorting process for best results, true in situ retorts and
horizontal and other shaped underground retorts can be used, if
desired, to retort oil shale and produce purge mode off gases for
use in upgrading the shale oil in a reactor. Furthermore, while it
is preferred to commence pulsed combustion at the top of the bed of
shale in the retort, in some circumstances it may be desirable to
commence pulsing at other sections of the retort.
Among the many advantages of the process are:
1. Better process efficiency.
2. Continuous upgrading of shale oil.
3. More effective use of processing equipment.
4. Greater retorting economy.
5. Less purification and treatment of retort water.
6. Improved product yield and recovery.
7. Uniformity of flame front.
8. Fewer oil fires.
9. Less loss of product oil.
10. Decreased carbonate decomposition and thermal cracking of the
effluent shale oil.
11. Reduced need for supplemental fuel gas, feed gas, and purge
gas.
12. Lower upgrading costs.
Although embodiments of this invention have been shown and
described, it is to be understood that various modifications and
substitutions, as well as rearrangements and combinations of
retorts, apparatus, and/or process steps, can be made by those
skilled in the art without departing from the novel spirit and
scope of this invention.
* * * * *